The present invention relates to a new and improved construction of make-and-break ignition plug--hereinafter simply referred to as break ignition plug--for piston engines which is of the type wherein an electromagnet acts upon an armature which actuates a movable electrode and an ignition pulse flows through the magnet coil of the electromagnet and a short-circuit path between the movable electrode and a counterelectrode (ground electrode), the magnetic field which builds-up in the electromagnet causing breaking of the short-circuit path in the presence of spark formation, there further being provided a pressure equalization chamber which communicates with an internal cylinder compartment of the piston motor or internal combustion engine in order to relieve the forces which are to be applied by the armature for the movement of the movable electrode.
Although break ignition plugs generate powerful ignition sparks at relatively low voltages, they have not found wide spread acceptance in practice. Apart from a pronounced burning-off of the electrodes, a freezing together of the interrupter contacts, sooting and similar disturbances, furthermore, the high and periodically alternating internal pressure of the cylinder causes considerable difficulties. In particular, the movable electrode must be shifted away by means of the armature from the stationary electrode in rapid time sequences, corresponding to the rotational speed of the piston motor or engine. This break movement is accomplished with the prior art break ignition plugs against the compression pressure, so that the armature and the magnet coil must be capable of applying relatively large forces. According to a state-of-the-art break ignition plug, as taught in German Pat. No. 1,919,828, the difficulties which are predicated upon the internal pressure of the cylinder are extensively overcome due to the construction of a pressure equalization chamber over the magnet coil. The pressurized gas which flows out of the internal compartment of the cylinder into the pressure equalization chamber thus reduces the forces which are to be applied by the armature, because such essentially only must still apply the mass force for propelling away the movable electrode, but otherwise need not overcome any additional pressure forces. Due to the ascent of the pressure gas into the upper region of the ignition plug past the magnet coil, the upper portion of the ignition plug however tends to heat up rather intensively, the pressure equalization chamber is located at a relatively large distance from the internal compartment of the cylinder and the gases must flow through large bores before they are effective.